186 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



wood, 1906), and Circaeaster (Junell, 1931) the pollen tube enters 

 through the funiculus or the integument. This is known as mes- 



ogamy. 



Formerly considerable phylogenetic significance was attached 

 to the route taken by the pollen tube during its entry into the 

 ovule, but now this point is considered to be of physiological 

 rather than phylogenetic importance, for we sometimes find con- 

 siderable variation in this respect even in one and the same species. 

 In Brassica oleracea (Thompson, 1933) the tube normally enters 



through the micropyle, but some- 

 times it may do so by way of 

 the chalaza. In Ulmus, Shat- 

 tuck (1905) speaks of its branch- 

 ing and apparently aimless wand- 

 ering through the funiculus, the 

 integuments, and occasionally 

 the nucellus. In Ep Hob turn 

 (Werner, 1914; Tackholm, 1915) 

 it may enter either through the 

 micropyle, through the integu- 

 ments, or by an intermediate 

 route. In Boerhaavia (Mahesh- 

 wari, 1929), although the tube 

 actually enters through the mi- 

 cropyle, it first makes a horizon- 

 tal crossing through the funicu- 

 lus. In Gossypium (Gore, 1932) 

 it often passes from the funiculus 

 to the base of the ovule and then 

 travels up along the wall of the 

 latter to enter the micropyle. 



An organ of special signifi- 

 cance in facilitating the entry of 

 the pollen tube into the ovule is 

 the so-called obturator, to which 

 reference had already been made 

 by Hofmeister in the year 1849. 



Fig. 110. Origin and structure of obtu- 

 rator in Myriocarpa longipes (A), Leu- 

 cosyke capitellata (B), and Quisqualis 



indica (C, D). (After Fagerlind 19U, Usually it is a swelling of the 

 1941.) placenta which grows towards 



